Smoking device with heating profile based on puff frequency

ABSTRACT

A method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session is provided, the aerosol-generating device including a power supply arranged to supply power to a heater during the usage session, the method including: using control electronics of the aerosol-generating device to associate a puff applied in the usage session with a corresponding target operating temperature for the heater based on a cumulative puff count of the applied puff in the usage session and on a time interval between the applied puff and an earlier puff applied in the usage session, and for the applied puff, control the supply of power from the power supply in order to adjust a temperature of the heater to the target operating temperature associated with the applied puff.

The present disclosure relates to a method of operating an aerosol-generating device, a computer-readable medium for use in an aerosol-generating device, an aerosol-generating device, as well as an aerosol-generating system.

Aerosol-generating devices configured to generate an aerosol from an aerosol-forming substrate, such as a tobacco-containing substrate, are known in the art. Typically, an inhalable aerosol is generated by the transfer of heat from a heat source to a physically separate aerosol-forming substrate or material, which may be located within, around or downstream of the heat source. An aerosol-forming substrate may be a liquid substrate contained in a reservoir. An aerosol-forming substrate may be a solid substrate. An aerosol-forming substrate may be a component part of a separate aerosol-generating article configured to engage with an aerosol-generating device to form an aerosol. During consumption, volatile compounds are released from the aerosol-forming substrate by heat transfer from the heat source and entrained in air drawn through the aerosol-generating article. As the released compounds cool, they condense to form an aerosol that is inhaled by the consumer.

Some aerosol-generating devices are configured to provide user experiences that have a finite duration. The duration of a usage session may be limited, for example, to approximate the experience of consuming a traditional cigarette. Some aerosol-generating devices are configured to be used with separate, consumable, aerosol-generating articles. Such aerosol-generating articles comprise an aerosol-forming substrate or substrates that are capable of releasing volatile compounds that can form an aerosol. Aerosol-forming substrates are commonly heated to form an aerosol. As the volatile compounds in an aerosol-forming substrate are depleted, the quality of the aerosol produced may deteriorate. Thus, some aerosol-generating devices are configured to limit the duration of the usage session to help prevent generation of a lower quality aerosol from a substantially depleted aerosol-forming substrate of an aerosol-generating article. A user would inhale aerosol from such a known aerosol-generating device by the application of one or more puffs to the device during the usage session. Some known aerosol-generating devices may limit the duration of the usage session based upon when a number of puffs applied to the device in the session reaches a predetermined limit.

It is known to provide power to a heat source to heat an aerosol-forming substrate in accordance with a thermal profile which varies over the duration of a usage session. In effect, such known thermal profiles define a temperature variation for the heat source as a function of the time elapsed in the usage session. As an aerosol-forming substrate becomes more depleted during a usage session, more energy is required to extract the remaining volatile compounds of the substrate which form the aerosol. Thus, it is known to use a thermal profile which increases a target operating temperature for the heat source over the second half of a usage session. Known thermal profiles used in the operation of a heat source are based on an idealised, hypothetical usage session. The idealised usage session may be characterised by a predetermined length for the usage session. The idealised usage session may additionally be based upon an assumed or idealised puffing behaviour of a user; for example, on an assumption that successive puffs are applied at a predetermined rate over a finite period of time. However, when a real-life usage session departs from the assumptions inherent in the idealised usage session, the use of such known thermal profiles to control the temperature of the heat source can lead to inefficient extraction of aerosol from the substrate and be detrimental to the overall user experience. By way of example, if a user applied puffs at a faster rate than assumed in the known thermal profile, this could result in the usage session being terminated earlier than anticipated in the idealised usage session. Consequently, the temperature of the heat source may never reach the levels required in the second half of the usage session to efficiently extract aerosol from the substrate.

It is therefore desired to overcome the deficiencies and limitations outlined above.

According to a first aspect of the present invention, there is provided a method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising a power supply arranged to supply power to a heater during the usage session. The method comprises:

associating a puff applied in the usage session with a corresponding target operating temperature for the heater based on a cumulative puff count of the applied puff in the usage session; and

for the applied puff, controlling the supply of power from the power supply in order to adjust a temperature of the heater to the target operating temperature associated with the applied puff.

By associating an applied puff with a corresponding target operating temperature for the heater based on cumulative puff count, it is possible to adjust the target operating temperature of the heater to take account of the specific puff characteristics of an individual user. This contrasts with known devices and thermal profiles discussed above, in which the temperature of the heater is varied as a function of the time elapsed in a usage session. The ability to adjust the target operating temperature of the heater according to the specific puff characteristics of an individual user may allow for more efficient extraction of aerosol from the aerosol-forming substrate. Efficient aerosol extraction from the substrate may be achieved regardless of (or with less dependence on) the rate at which an individual user applies puffs to the aerosol-generating device. Therefore, a user may be able to extract substantially all aerosol from the substrate without being limited to applying puffs at a predetermined rate. These advantages may also provide the user with an enhanced user experience over the usage session.

As used herein, the term “aerosol-generating device” refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-forming substrate may be part of an aerosol-generating article, for example part of a smoking article. An aerosol-generating device may comprise one or more components used to supply energy from a power supply to an aerosol-forming substrate to generate an aerosol. For example, an aerosol-generating device may be a heated aerosol-generating device. An aerosol-generating device may be an electrically heated aerosol-generating device or a gas-heated aerosol-generating device. An aerosol-generating device may be a smoking device that interacts with an aerosol-forming substrate of an aerosol-generating article to generate an aerosol that is directly inhalable into a user's lungs through the user's mouth.

As used herein, the term “aerosol-forming substrate” refers to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may be solid or liquid or comprise both solid and liquid components. An aerosol-forming substrate may be adsorbed, coated, impregnated or otherwise loaded onto a carrier or support. An aerosol-forming substrate may conveniently be part of an aerosol-generating article or smoking article.

An aerosol-forming substrate may comprise nicotine. An aerosol-forming substrate may comprise tobacco, for example may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. In preferred embodiments an aerosol-forming substrate may comprise homogenised tobacco material, for example cast leaf tobacco. An aerosol-forming substrate may comprise at least one aerosol-former, such as propylene glycol or glycerine.

As used herein, the term “usage session” refers to a period in which a series of puffs are applied by a user to extract aerosol from an aerosol-forming substrate.

As used herein, the term “cumulative puff count” refers to the number of puffs applied by a user in a usage session, relative to the start of that usage session.

Conveniently, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, wherein the target operating temperature associated with the applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff. In this manner, the temperatures of the predetermined thermal profile are linked to puff count. This contrasts with the known devices discussed above, in which the thermal profile temperatures are linked solely to the elapsed time in a usage session.

The predetermined thermal profile may be stored in a controller used to control the power supply. Alternatively, the predetermined thermal profile may be stored in a memory module accessible to such a controller.

Advantageously, the predetermined thermal profile may comprise a predetermined relationship between a puff parameter and the predetermined distribution of puffs. The method may further comprise: determining if a value of the puff parameter for either or both the applied puff and an earlier puff applied in the usage session differs from a value of the puff parameter for corresponding puffs of the predetermined distribution of puffs; modifying the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using the determined difference in the value of the puff parameter; and using the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff. In this manner, the predetermined thermal profile may be dynamically adapted during a usage session in response to characteristics of the puffs applied by an individual user during the usage session.

As described in more detail below, the puff parameter used in modifying the thermal profile may comprise one or more of: i) a time interval between successive puffs; ii) an intensity of a puff; and iii) a volume of aerosol generated from the aerosol-forming substrate in response to a puff.

The time interval between successive applied puffs is preferably determined by a controller based upon detection of each puff. The controller may contain control electronics configured to measure the time interval. Puff detection may be performed directly by use of an airflow sensor or the like. Preferably however, puff detection is performed indirectly based upon detecting a temperature change in the heater which would be expected to accompany any applied puff. Determination of a temperature of the heater may be performed directly by use of a temperature sensor. Preferably however, the temperature of the heater is determined indirectly based upon a change in one or more operating parameters of the aerosol-generating device. For example, the temperature of the heater may be determined based upon an electrical resistance of the heater; this is particularly relevant to where the heater is a resistive heater. In another example, if the heater takes the form of a susceptor which in use is heated by an inductor, the temperature of the susceptor may be determined based upon changes in the current supplied to the inductor from the power supply.

The volume of aerosol generated in response to an applied puff may be determined directly or indirectly. The volume may be determined directly by use of an airflow sensor or the like. Preferably however, the volume is determined indirectly by use of a parameter indicative of aerosol generation during a usage session. The parameter indicative of aerosol generation may itself by representative of power supplied by the power supply during the usage session. For example, current, voltage, or both current and voltage supplied to the heater may be parameters representative of power. For example, the power supply may supply power to maintain the heater at a predetermined temperature during the usage session. If a user puffs on the aerosol-generating device to generate an aerosol, the heater cools and a greater amount of power is required to maintain the heater at the predetermined temperature. So, by monitoring a parameter representative of power supplied by the power supply, a value indicative of real time aerosol generation may be recorded.

Advantageously, there may be a predetermined threshold limit for the thermal profile, above which the temperatures of the thermal profile cannot be modified. By way of example, modification of the temperatures in the thermal profile may be limited to a change in temperature of no more than a predetermined threshold limit of +/−10%, or +/−7.5%, or +/−5%, or +/−3% of the unmodified temperature. The provision of a threshold limit for modifying the temperatures of the thermal profile helps to avoid excessive temperature fluctuations in the heater (and substrate) between successive applied puffs. Additionally or alternatively, the predetermined threshold limit may comprise an absolute temperature limit. The value of this absolute temperature limit may be set so as to avoid ignition and combustion of the aerosol-forming substrate and the evolution of harmful compounds from the substrate. By way of example, the absolute temperature limit may be set to a value of 400 degrees Celsius, or 375 degrees Celsius, or 350 degrees Celsius.

The associating of the applied puff with a corresponding target operating temperature for the heater may additionally be based on a time interval between the applied puff and an earlier puff applied in the usage session. In this manner, the target operating temperature for the heater may be a function of both i) the cumulative puff count of the applied puff and ii) the time interval between the applied puff and an earlier puff. This functionality provides an ability to adjust the target operating temperature for the heater during a usage session to take account of the rate at which puffs are applied by an individual user during the session. This thereby enables efficient extraction of aerosol from the substrate to be maintained over the usage session regardless of (or with less dependence on) the time interval between successive applied puffs. Preferably, the earlier puff is the immediate predecessor to the applied puff in the usage session.

Each puff applied by a user will itself have a finite duration. Preferably, the time interval between the applied puff and an earlier puff in the usage session is the time interval between initiation of the applied puff and initiation of the earlier puff. Alternatively however, the time interval between the applied puff and an earlier puff in the usage session may be the time interval between termination of the applied puff and termination of the earlier puff.

As described above, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs. Preferably, the predetermined thermal profile comprises a predetermined time spacing between successive puffs of the predetermined distribution of puffs. The method may further comprise: determining if the time interval between the applied puff and the earlier puff differs from the predetermined time spacing between corresponding puffs of the predetermined distribution of puffs; modifying the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this time difference; and using the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff. In this manner, the temperatures of the predetermined thermal profile can be modified based upon the actual, real-time puff behaviour of a user so as to maintain efficient aerosol extraction from the substrate. As described above, the predetermined thermal profile may be stored in a controller used to control the power supply. Alternatively, the predetermined thermal profile may be stored in a memory module accessible to such a controller. The predetermined time spacing may be uniform across the predetermined distribution of puffs.

A non-limiting example of the use and modification of a predetermined thermal profile employing such a “predetermined time spacing” between successive puffs of a predetermined distribution of puffs is now described: The predetermined distribution of puffs of the thermal profile may have successive puffs spaced apart from each other by a time interval of Δt_(predet). So, a puff ‘n’ would be separated from its successor puff ‘n+1’ in time by Δt_(predet) in the thermal profile. Conveniently, the time interval Δt_(predet) is 30 seconds. However, other values for the time interval Δt_(predet) may be chosen according to the rate at which an idealised or hypothetical user is assumed to apply puffs over the course of a usage session. In this example, the thermal profile defines the heater temperature for puffs ‘n’ and ‘n+1’ as T_(n) and T_(n+1) respectively. In the thermal profile, T_(n) and T_(n+)1 are different to each other and spaced apart from each other by the time interval of Δt_(predet).

Two scenarios are now considered in which an actual user applies puffs to the device over the course of a usage session: In a first scenario, the user applies puffs in accordance with the predetermined time spacing of the thermal profile, meaning that each puff is spaced apart from its predecessor by Δt_(predet). In this first scenario, the target operating temperature for the heater for applied puff ‘n+1’ would simply correspond to temperature T_(n+1), with no modification required to the thermal profile. In a second scenario, the same user applies puffs at a faster or slower rate than assumed in the thermal profile. In this second scenario, the temperature of the thermal profile for puff ‘n+1’ is modified according to whether the user has applied puff ‘n+1’ sooner or later than assumed in the thermal profile, i.e. according to whether the applied puffs ‘n’, ‘n+1’ are separated in time by less than or more than time interval Δt_(predet). Preferably, the temperature of the thermal profile corresponding to puff ‘n+1’ is modified according to how much sooner or later puff ‘n+1’ is applied after puff ‘n’ relative to time interval Δt_(predet). Advantageously, the temperature of the thermal profile corresponding to puff ‘n+1’ is modified in proportion to how much sooner or later puff ‘n+1’ is applied after puff ‘n’ relative to Δt_(predet).

The associating of the applied puff with a corresponding target operating temperature for the heater may additionally be based on an intensity of an earlier puff applied in the usage session. In this manner, the target operating temperature for the heater may consequently be a function of both i) the cumulative puff count of the applied puff and ii) the intensity of an earlier puff. Optionally, the target operating temperature may additionally be a function of a time interval between the applied puff and an earlier puff, as described in the preceding paragraphs. Puff intensity can affect both depletion of the aerosol-forming substrate and the temperature of the substrate. The greater the intensity of a puff applied by a user, the more aerosol is generated in response to that puff and the more the substrate becomes depleted of those compounds necessary for aerosol formation. Further, a puff of higher than expected intensity may cause cooling of the substrate below a level needed to ensure efficient extraction of aerosol from the substrate. As the substrate becomes more depleted, more energy—and consequently a higher heater temperature—is required to extract the remaining compounds necessary for aerosol formation. So, having the associating of the applied puff with a corresponding target operating temperature for the heater being additionally based on an intensity of an earlier puff provides a benefit of enabling the target operating temperature to be adjusted to counter substrate depletion caused by the intensity characteristics of the puffs applied by an individual user. This thereby enables efficient extraction of aerosol from the substrate to be maintained regardless of (or with less dependence) on the intensity of puffs applied by the user. Preferably, the earlier puff immediately precedes the applied puff in the usage session.

The intensity of a given puff can be characterised in various ways. By way of example, the intensity of a puff may be characterised by the volume of aerosol generated from the substrate in response to that puff. Accordingly, the method may further comprise: determining a volume of aerosol generated from the aerosol-forming substrate in response to the earlier puff, and using the determined volume to determine the intensity of the earlier puff.

As described above, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs. Preferably, the predetermined thermal profile comprises a predetermined intensity for each puff of the predetermined distribution of puffs. The method may further comprise: determining if the intensity of the earlier puff differs from the predetermined intensity for the corresponding puff of the predetermined distribution of puffs; modifying the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this intensity difference; and using the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff. In this manner, the predetermined thermal profile can be adapted in real-time according to the puff intensity characteristics of an individual user so as to maintain efficient extraction of aerosol from the substrate. As described above, the predetermined thermal profile may be stored in a controller used to control the power supply. Alternatively, the predetermined thermal profile may be stored in a memory module accessible to such a controller. The predetermined intensity may be uniform across the predetermined distribution of puffs.

A non-limiting example of the use and modification of a predetermined thermal profile which employs such a “predetermined intensity” for each puff of the predetermined distribution of puffs is now described. In this example, the volume of aerosol generated in response to a puff is used as a measure of the puff intensity: For the predetermined thermal profile, the predetermined distribution of puffs consists of a predetermined number, N, of puffs applied over the course of a hypothetical usage session. The thermal profile also defines a predetermined total volume, V, of aerosol produced from an aerosol-forming substrate over the course of the hypothetical usage session. For the purposes of this example, the predetermined total aerosol volume, V, is assumed to be generated evenly over each of the N puffs. So, in the predetermined thermal profile, each puff of the ‘N’ puffs is assumed to result in generation of the same volume, v, of aerosol, where v=V/N. In this example, volume, v, corresponds to the “predetermined intensity”.

Two scenarios are now considered of an actual user applying puffs to the device over the course of a usage session: In a first scenario, the user applies puffs in accordance with the predetermined distribution of puffs of the thermal profile. This means that each puff applied by the user during the usage session has an intensity which conforms to the thermal profile, i.e. each applied puff results in generation of volume, v, of aerosol. In this first scenario, no modification to the thermal profile would occur, with the target operating temperature for the heater for each applied puff simply tracking the corresponding temperature in the thermal profile for the puff in the predetermined distribution of puffs corresponding in number to the cumulative puff count of the applied puff. However, in a second scenario, the user may apply puffs which differ in intensity (and therefore in volume of aerosol generated) from the assumptions made in the thermal profile. In this second scenario, two successive puffs applied by a user are monitored: puffs ‘n’ and ‘n+1’. If applied puff ‘n’ has an intensity stronger than assumed in the thermal profile, then the aerosol volume, v_(n), resulting from puff ‘n’ would be greater than the idealised volume, v, of the thermal profile. The greater than expected intensity (aerosol volume v_(n)) for puff ‘n’ would result in greater than expected depletion of the substrate in response to puff ‘n’. To compensate for the greater than expected depletion, the target operating temperature for the next puff ‘n+1’ may need to be higher than is defined in the predetermined thermal profile. Alternatively, if applied puff ‘n’ has an intensity weaker than assumed in the thermal profile, then the aerosol volume, v_(n), for puff ‘n’ would be less than the idealised volume, v, of the thermal profile. The less than expected intensity (aerosol volume v_(n)) for puff ‘n’ would result in less than expected depletion of the substrate in response to puff ‘n’. To compensate for the lower than expected depletion, the target operating temperature for the next puff ‘n+1’ may need to be lower than is defined in the predetermined thermal profile. The modification of the temperature for puff ‘n+1’ in the predetermined thermal profile can be expressed as follows:

T _(n+1) ^(modified) =T _(n+1).∝  Equation 1

for which: T_(n+1) is the temperature initially defined in the thermal profile for puff ‘n+1’ T_(n+1) ^(modified) is the modified temperature of the thermal profile for puff ‘n+1’; and α is a correction factor applied to T_(n+1) to address the actual “intensity” of puff ‘n’. The correction factor α may vary dependent on the amount by which the volume of aerosol, v_(n), produced in response to applied puff ‘n’ is greater than or less than idealised volume, v.

In one example, the correction factor, α, may be expressed as follows:

$\begin{matrix} {\propto {= \left\lbrack \left( {1 + {\delta.\left( \frac{v_{n} - v}{v} \right)}} \right) \right\rbrack}} & {{Equation}2} \end{matrix}$

for which: δ is a scale factor, whose value may be chosen so as to increase or reduce the effect of v_(n) being different to v when modifying the initially defined temperature T_(n+1).

The associating of the applied puff with a corresponding target operating temperature for the heater may additionally be based on a volume of aerosol generated from the aerosol-forming substrate in response to an earlier puff applied in the usage session. In this manner, the target operating temperature for the heater may consequently be a function of both i) the cumulative puff count of the applied puff and ii) the volume of aerosol generated in response to an earlier puff. Optionally, the target operating temperature may additionally be a function of one or more of i) a time interval between the applied puff and the earlier puff (as described in the preceding paragraphs), and ii) an intensity of the earlier puff (as described in the preceding paragraphs). This can be understood to be closely related to the situation described above of the target operating temperature being a function of puff intensity, with the volume of aerosol generated in response to a puff being one suitable means of characterising an intensity of that puff. The greater the volume of aerosol generated in response to a puff, the more the substrate becomes depleted. As the substrate becomes more depleted, more energy—and consequently a higher heater temperature—is required to extract the remaining compounds necessary for aerosol formation. So, having the associating of the applied puff with a corresponding target operating temperature for the heater being additionally based on a volume of aerosol generated in response to an earlier puff provides a benefit of enabling the target operating temperature to be adjusted to counter substrate depletion caused by the characteristics of the puffs applied by an individual user. Preferably, the earlier puff immediately precedes the applied puff in the usage session.

As described above, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs. Preferably, the predetermined thermal profile comprises a predetermined volume of aerosol generated from the aerosol-forming substrate for each puff of the predetermined distribution of puffs. The method may further comprise determining if the volume of aerosol generated for the earlier puff differs from the predetermined volume for the corresponding puff of the predetermined distribution of puffs; modifying the temperature of the predetermined temperature profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this volume difference; and using the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff. In this manner, the predetermined thermal profile can be adapted according to the puff characteristics of an individual user, thereby facilitating maintaining efficient extraction of aerosol from the substrate over a usage session. As described above, the predetermined thermal profile may be stored in a controller used to control the power supply. Alternatively, the predetermined thermal profile may be stored in a memory module accessible to such a controller. The predetermined volume may be uniform across the predetermined distribution of puffs. The non-limiting example outlined in the preceding paragraphs with reference to Equations 1 and 2 describing the use and modification of a predetermined thermal profile which employs a “predetermined intensity” for each puff of the predetermined distribution of puffs is also applicable to the variant described in this paragraph of the predetermined thermal profile employing a “predetermined volume” of aerosol generated.

Conveniently, the target operating temperature varies over the usage session within a range of 320 degrees Celsius to 350 degrees Celsius. Such an operating temperature has been found especially suitable when generating aerosol from aerosol-forming substrates which are solid and comprise tobacco. However, the present disclosure is not limited to the use of solid aerosol-forming substrates, and may also be applied to use with liquid aerosol-forming substrates. It is also desirable to limit a maximum value for the target operating temperature over the usage session so as to avoid ignition and combustion of the substrate and the evolution of harmful compounds from the substrate; by way of example, this limit may be set at 400 degrees Celsius, or 375 degrees Celsius, or 350 degrees Celsius. The specific range and limit for target operating temperature over a usage session may be set according to the heating characteristics of the specific aerosol-forming substrate which is used, as well as the energy capacity of the power source which is used.

The method may comprise detecting the applied puff by monitoring a change in heater temperature in response to the applied puff. By way of example, the heater temperature may be detected as described in the preceding paragraphs.

The method may further comprise terminating the usage session upon the first to occur of: i) a cumulative number of puffs applied in the usage session reaching a predetermined puff limit, or ii) the usage session reaching a predetermined maximum time duration. By way of example, the predetermined puff limit may be 12 puffs and the predetermined maximum time duration be 6 minutes. However, other values for the puff limit and maximum time duration may be set, with their selection affected by a number of factors. These factors may include the amount and composition of aerosol-forming substrate which is used and the amount of power available from the power supply in a given usage session. It is preferable for the aerosol-generating device to be portable and to have a size and a mass suitable for the device to be held by the hand of a user. These preferences will, in turn, affect the size and energy capacity of the power source of the aerosol-generating device, which will thereby affect the values set for the puff limit and maximum time duration.

According to a second aspect of the present invention, there is provided a computer-readable medium for use in an aerosol-generating device, the computer-readable medium containing instructions for performing the method of the first aspect and any of its variants as described above. The computer-readable medium may comprise a computer memory. The computer-readable medium may be provided in a controller used to control the power supply. Alternatively, the computer-readable medium may be a discrete component separate to but accessible to such a controller. Preferably, the computer-readable medium is both readable and writable in use, which thereby provides a benefit of enabling a thermal profile stored in the computer-readable medium to be modified during the course of a usage session.

According to a third aspect of the present invention, there is provided an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session. The aerosol-generating device comprises:

-   -   a power supply arranged to supply power to a heater during the         usage session; the aerosol-generating device configured to:     -   associate a puff applied in the usage session with a         corresponding target operating temperature for the heater based         on a cumulative puff count of the applied puff in the usage         session; and     -   for the applied puff, control the supply of power from the power         supply in order to adjust a temperature of the heater to the         target operating temperature associated with the applied puff.

This third aspect provides an aerosol-generating device which, in general terms, is able to perform the method of the first aspect and its variants described above. For completeness, different variants of the aerosol-generating device are briefly outlined below.

As described above in relation to the first aspect, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the aerosol-generating device configured such that the target operating temperature associated with the applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff.

As described above in relation to the first aspect, the predetermined thermal profile may be stored in a controller used to control the power supply. Alternatively, the predetermined thermal profile may be stored in a memory module accessible to such a controller.

As described above in relation to the first aspect, the predetermined thermal profile may comprise a predetermined relationship between a puff parameter and the predetermined distribution of puffs. Further, the aerosol-generating device is preferably configured to:

determine if a value of the puff parameter for either or both the applied puff and an earlier puff differs from a value of the puff parameter for corresponding puffs of the predetermined distribution of puffs; modify the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this difference in the value of the puff parameter; and use the modified heater temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff.

As described for the first aspect, the puff parameter may comprise one or more of: a time interval between successive puffs; an intensity of a puff; and a volume of aerosol generated from the aerosol-forming substrate in response to a puff.

The provision of a predetermined threshold limit for the thermal profile as described for the first aspect is equally applicable to the aerosol-generating device of this third aspect of the invention.

The aerosol-generating device may also be configured: to determine a time interval between the applied puff and an earlier puff; and such that the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on the determined time interval.

As previously described, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs. Preferably, the predetermined thermal profile comprises a predetermined time spacing between successive puffs of the predetermined distribution of puffs, with the aerosol-generating device configured to: determine if the determined time interval between the applied puff and the earlier puff differs from the predetermined time spacing between corresponding puffs of the predetermined distribution of puffs; modify the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this time difference; and use the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff. The example described in the preceding paragraphs (for the method of the first aspect) of the use and modification of a predetermined thermal profile employing a “predetermined time spacing” between successive puffs of a predetermined distribution of puffs is equally applicable to providing an understanding of the configuration of the device outlined in this paragraph.

The aerosol-generating device may also be configured to: determine an intensity of an earlier puff applied in the usage session; and such that the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on the determined intensity of the earlier puff. As discussed in the preceding paragraphs for the first aspect, the intensity of a given puff can be characterised in various ways. By way of example, the intensity of a puff may be characterised by the volume of aerosol generated from the substrate in response to that puff. Accordingly, the aerosol-generating device may be configured to: determine a volume of aerosol generated from the aerosol-forming substrate in response to the earlier puff; and use the determined volume in determining the intensity of the earlier puff.

As described above, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs. Preferably, the predetermined thermal profile comprises a predetermined intensity for each puff of the predetermined distribution of puffs, with the aerosol-generating device configured to: determine if the determined intensity of the earlier puff differs from the predetermined intensity for the corresponding puff of the predetermined distribution of puffs; modify the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this intensity difference; and use the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff. The example described in the preceding paragraphs (for the method of the first aspect) of the use and modification of a predetermined thermal profile employing a “predetermined intensity” for each puff of a predetermined distribution of puffs is equally applicable to providing an understanding of the configuration of the device outlined in this paragraph.

The aerosol-generating device may also be configured: to determine a volume of aerosol generated from the aerosol-forming substrate in response to an earlier puff applied in the usage session; and such that the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on the determined volume for the earlier puff. As noted in previous paragraphs, this is closely related to the situation described above of the target operating temperature being a function of puff intensity, with the volume of aerosol generated in response to a puff being one suitable means of characterising the intensity of that puff.

As described above, the aerosol-generating device may store a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs. Preferably, the predetermined thermal profile comprises a predetermined volume of aerosol generated from the aerosol-forming substrate for each puff of the predetermined distribution of puffs, with the aerosol-generating device configured to: determine if the determined volume of aerosol generated for the earlier puff differs from the predetermined volume for the corresponding puff of the predetermined distribution of puffs; modify the temperature of the predetermined temperature profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this volume difference; and use the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff.

In a similar manner and for the same reasoning as discussed in preceding paragraphs for the method of the first aspect, the aerosol-generating device may be configured such that the target operating temperature is restricted to vary within a range of 320 degrees Celsius to 350 degrees Celsius.

The aerosol-generating device may be configured to detect the applied puff by monitoring a change in heater temperature in response to the applied puff.

In a similar manner and for the same reasoning as discussed in preceding paragraphs for the method of the first aspect, the aerosol-generating device may also be configured to terminate the usage session upon the first to occur of: i) a cumulative number of puffs applied in the usage session reaching a predetermined puff limit, or ii) the usage session reaching a predetermined maximum time limit duration.

The aerosol-generating device may comprise the heater. By way of example, the heater may be a resistive heating element which is intended to fit around or within an aerosol-forming substrate. Alternatively, the heater may be distinct and separate to the device. For example, the heater may be a susceptor forming part of an article distinct from the device, in which the article houses the aerosol-forming substrate. In such an example, the aerosol-generating device may comprise an inductor, with the power supply configured to provide power to the inductor such that, in use of the device with the article, the inductor would induce eddy currents into the susceptor, thereby resulting in heating of the susceptor.

In a fourth aspect, there is provided an aerosol-generating system, the system comprising the aerosol-generating device according to the third aspect and any of its variants described above and an aerosol-generating article, the aerosol-generating article comprising the heater and aerosol-forming substrate, wherein the aerosol-generating device is configured to receive the aerosol-generating article.

By way of example, the heater may be in the form of a susceptor, with the aerosol-generating device comprising an inductor coupled to the power supply. The aerosol-generating article and device are preferably configured such that when the article is received by the device, the inductor and susceptor are positioned relative to each other so that the provision of power from the power supply to the inductor induces eddy currents into the susceptor, thereby causing heating of the aerosol-forming substrate.

The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

Example Ex1: A method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising:

-   -   a power supply arranged to supply power to a heater during the         usage session;     -   the method comprising:     -   associating a puff applied in the usage session with a         corresponding target operating temperature for the heater based         on a cumulative puff count of the applied puff in the usage         session; and     -   for the applied puff, controlling the supply of power from the         power supply in order to adjust a temperature of the heater to         the target operating temperature associated with the applied         puff.

Example Ex2: A method according to Ex1, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, wherein the target operating temperature associated with the applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff.

Example Ex3: A method according to Ex2, the predetermined thermal profile comprising a predetermined relationship between a puff parameter and the predetermined distribution of puffs; the method further comprising:

-   -   determining if a value of the puff parameter for either or both         the applied puff and an earlier puff applied in the usage         session differs from a value of the puff parameter for         corresponding puffs of the predetermined distribution of puffs;     -   modifying the temperature of the predetermined thermal profile         for the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using the determined difference in the value of the puff         parameter; and     -   using the modified temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Example Ex4: A method according to Ex3, in which the puff parameter comprises one or more of:

-   -   a time interval between successive puffs;     -   an intensity of a puff; and     -   a volume of aerosol generated from the aerosol-forming substrate         in response to a puff.

Example Ex5: A method according to any one of Ex1 to Ex4, wherein the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on a time interval between the applied puff and an earlier puff applied in the usage session.

Example Ex6: A method according to Ex5, in which the earlier puff immediately precedes the applied puff in the usage session.

Example Ex7: A method according to either one of Ex5 or Ex6, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined time spacing between successive puffs of the predetermined distribution of puffs;

-   -   the method further comprising:     -   determining if the time interval between the applied puff and         the earlier puff differs from the predetermined time spacing         between corresponding puffs of the predetermined distribution of         puffs;     -   modifying the temperature of the predetermined thermal profile         for the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using this time difference; and     -   using the modified temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Ex8: A method according to Ex7, in which the predetermined time spacing is non-uniform across the predetermined distribution of puffs.

Ex9: A method according to any one of Ex1 to Ex8, wherein the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on an intensity of an earlier puff applied in the usage session.

Ex10: A method according to Ex9, in which the earlier puff is the immediate predecessor to the applied puff.

Ex11: A method according to either one of Ex9 or Ex10, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined intensity for each puff of the predetermined distribution of puffs;

-   -   the method further comprising:     -   determining if the intensity of the earlier puff differs from         the predetermined intensity for the corresponding puff of the         predetermined distribution of puffs;     -   modifying the temperature of the predetermined thermal profile         for the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using this intensity difference; and     -   using the modified temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Ex12: A method according to Ex11, in which the predetermined intensity is non-uniform across the predetermined distribution of puffs.

Ex13: A method according to any one of Ex9 to Ex12, the method further comprising:

-   -   determining a volume of aerosol generated from the         aerosol-forming substrate in response to the earlier puff, and         using the determined volume to determine the intensity of the         earlier puff.

Ex14: A method according to any one of Ex1 to 13, wherein the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on a volume of aerosol generated from the aerosol-forming substrate in response to an earlier puff applied in the usage session.

Ex15: A method according to Ex14, in which the earlier puff is the immediate predecessor to the applied puff.

Ex16: A method according to either one of Ex14 or Ex15, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined volume of aerosol generated from the aerosol-forming substrate for each puff of the predetermined distribution of puffs;

-   -   the method further comprising:     -   determining if the volume of aerosol generated for the earlier         puff differs from the predetermined volume for the corresponding         puff of the predetermined distribution of puffs;     -   modifying the temperature of the predetermined temperature         profile for the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using this volume difference; and     -   using the modified temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Ex17: A method according to Ex16, in which the predetermined volume is non-uniform across the predetermined distribution of puffs.

Ex18: A method according to any one of Ex1 to Ex17, in which the target operating temperature varies over the usage session within a range of 320 degrees Celsius to 350 degrees Celsius.

Ex19: A method according to any one of Ex1 to Ex18, the method comprising detecting the applied puff by monitoring a change in heater temperature in response to the applied puff.

Ex20: A method according to any one of Ex1 to Ex19, the method further comprising terminating the usage session upon the first to occur of:

-   -   i) a cumulative number of puffs applied in the usage session         reaching a predetermined puff limit, or ii) the usage session         reaching a predetermined maximum time duration.

Ex21: A computer-readable medium for use in an aerosol-generating device, the computer-readable medium containing instructions for performing the method according to any one of Ex1 to Ex20.

Ex22: An aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising:

-   -   a power supply arranged to supply power to a heater during the         usage session;     -   the aerosol-generating device configured to:     -   associate a puff applied in the usage session with a         corresponding target operating temperature for the heater based         on a cumulative puff count of the applied puff in the usage         session; and     -   for the applied puff, control the supply of power from the power         supply in order to adjust a temperature of the heater to the         target operating temperature associated with the applied puff.

Ex23: An aerosol-generating device according to Ex22, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the aerosol-generating device configured such that the target operating temperature associated with the applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff.

Ex24: An aerosol-generating device according to Ex23, in which the predetermined thermal profile stored by the aerosol-generating device comprises a predetermined relationship between a puff parameter and the predetermined distribution of puffs; wherein the aerosol-generating device is configured to:

-   -   determine if a value of the puff parameter for either or both         the applied puff and an earlier puff differs from a value of the         puff parameter for corresponding puffs of the predetermined         distribution of puffs;     -   modify the temperature of the predetermined thermal profile for         the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using this difference in the value of the puff parameter; and     -   use the modified heater temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Ex25: An aerosol-generating device according to Ex24, in which the puff parameter comprises one or more of:

-   -   a time interval between successive puffs;     -   an intensity of a puff; and     -   a volume of aerosol generated from the aerosol-forming substrate         in response to a puff.

Ex26: An aerosol-generating device according to any one of Ex22 to Ex25, wherein the aerosol-generating device is configured:

-   -   to determine a time interval between the applied puff and an         earlier puff; and     -   such that the associating of the applied puff with a         corresponding target operating temperature for the heater is         additionally based on the determined time interval.

Ex27: An aerosol-generating device according to Ex26, wherein the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined time spacing between successive puffs of the predetermined distribution of puffs;

-   -   wherein the aerosol-generating device is configured to:     -   determine if the determined time interval between the applied         puff and the earlier puff differs from the predetermined time         spacing between corresponding puffs of the predetermined         distribution of puffs;     -   modify the temperature of the predetermined thermal profile for         the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using this time difference; and     -   use the modified temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Ex28: An aerosol-generating device according to any one of Ex22 to Ex27, the aerosol-generating device further configured:

-   -   to determine an intensity of an earlier puff applied in the         usage session; and such that the associating of the applied puff         with a corresponding target operating temperature for the heater         is additionally based on the determined intensity of the earlier         puff.

Ex29: An aerosol-generating device according to Ex28, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined intensity for each puff of the predetermined distribution of puffs;

-   -   wherein the aerosol-generating device is configured to:     -   determine if the determined intensity of the earlier puff         differs from the predetermined intensity for the corresponding         puff of the predetermined distribution of puffs;     -   modify the temperature of the predetermined thermal profile for         the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using this intensity difference; and     -   use the modified temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Ex30: An aerosol-generating device according to either one of Ex28 or Ex29, in which the aerosol-generating device is configured to:

-   -   determine a volume of aerosol generated from the aerosol-forming         substrate in response to the earlier puff; and     -   use the determined volume in determining the intensity of the         earlier puff.

Ex31: An aerosol-generating device according to any one of Ex22 to Ex30, the aerosol-generating device further configured:

-   -   to determine a volume of aerosol generated from the         aerosol-forming substrate in response to an earlier puff applied         in the usage session; and     -   such that the associating of the applied puff with a         corresponding target operating temperature for the heater is         additionally based on the determined volume for the earlier         puff.

Ex32: An aerosol-generating device according to Ex31, in which the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined volume of aerosol generated from the aerosol-forming substrate for each puff of the predetermined distribution of puffs;

-   -   wherein the aerosol-generating device is configured to:     -   determine if the determined volume of aerosol generated for the         earlier puff differs from the predetermined volume for the         corresponding puff of the predetermined distribution of puffs;     -   modify the temperature of the predetermined temperature profile         for the puff in the predetermined distribution of puffs         corresponding to the cumulative puff count of the applied puff         by using this volume difference; and     -   use the modified temperature of the predetermined thermal         profile as the target operating temperature associated with the         applied puff.

Ex33: An aerosol-generating device according to any one of Ex22 to Ex32, in which the aerosol-generating device is configured such that the target operating temperature is restricted to vary within a range of 320 degrees Celsius to 350 degrees Celsius.

Ex34: An aerosol-generating device according to any one of Ex22 to Ex33, in which the aerosol-generating device is configured to detect the applied puff by monitoring a change in heater temperature in response to the applied puff.

Ex35: An aerosol-generating device according to any one of Ex22 to Ex34, in which the aerosol-generating device is configured to terminate the usage session upon the first to occur of:

-   -   i) a cumulative number of puffs applied in the usage session         reaching a predetermined puff limit, or ii) the usage session         reaching a predetermined maximum time limit duration.

Ex36: An aerosol-generating device according to any of Ex22 to Ex35, in which the aerosol-generating device comprises the heater.

Ex37: An aerosol-generating system, the system comprising the aerosol-generating device according to any one of claims 22 to 35 and an aerosol-generating article, the aerosol-generating article comprising the heater and aerosol-forming substrate, wherein the aerosol-generating device is configured to receive the aerosol-generating article.

Examples will now be further described with reference to the figures, in which:

FIG. 1 illustrates a schematic side view of an aerosol-generating device;

FIG. 2 illustrates a schematic upper end view of the aerosol-generating device of FIG. 1 ;

FIG. 3 illustrates a schematic cross-sectional side view of the aerosol-generating device of FIG. 1 and an aerosol-generating article for use with the device;

FIG. 4 illustrates a prior art thermal profile used in the operation of known aerosol-generating devices;

FIG. 5 illustrates a variation in target operating temperature of a heater of an aerosol-generating device resulting from use of the prior art thermal profile of FIG. 4 , in a scenario in which a user applies successive puffs each spaced apart by 15 seconds;

FIG. 6 illustrates a variation in target operating temperature of a heater of an aerosol-generating device resulting from use of the prior art thermal profile of FIG. 4 , in a scenario in which a user applies successive puffs each spaced apart by 11 seconds;

FIG. 7 illustrates a method in accordance with the present disclosure, in which the target operating temperature for the heater is adjusted as a function of puff count;

FIG. 8 illustrates a thermal profile according to the present disclosure, in which the target operating temperature for the heater is defined as a function of puff count;

FIG. 9 illustrates how the target operating temperature of the heater is varied when using the thermal profile of FIG. 8 , in a scenario in which a user applies puffs at uniform intervals;

FIG. 10 illustrates how the target operating temperature of the heater is varied when using the thermal profile of FIG. 8 , in a scenario in which a user applies puffs at varying (i.e. non-uniform) intervals.

An exemplary aerosol-generating device 10 is a hand-held aerosol generating device, and has an elongate shape defined by a housing 20 that is substantially circularly cylindrical in form (see FIGS. 1, 2 and 3 ). The aerosol-generating device 10 comprises an open cavity 25 located at a proximal end 21 of the housing 20 for receiving an aerosol-generating article 30 comprising an aerosol-forming substrate 31. The aerosol-generating device 10 has a battery 26, control electronics 27 and a memory module 28 located within the housing 20. The memory module 28 is readable and writable in use. An electrically-operated heater 40 is arranged within the device 10 to heat at least an aerosol-forming substrate portion 31 of an aerosol-generating article 30 when the aerosol-generating article is received in the cavity 25. The memory module 28 stores a thermal profile accessible to the control electronics 27 during use of the device 10. The thermal profile defines how a target operating temperature for the heater 40 varies in a usage session.

The aerosol-generating device is configured to receive a consumable aerosol-generating article 30. The aerosol-generating article 30 is in the form of a cylindrical rod and comprises an aerosol-forming substrate 31 (see FIG. 3 ). The aerosol-forming substrate 31 is a solid aerosol-forming substrate comprising tobacco. The aerosol-generating article 30 further comprises a mouthpiece such as a filter 32 arranged in coaxial alignment with the aerosol-forming substrate 31 within the cylindrical rod. The aerosol-generating article 30 has a diameter substantially equal to the diameter of the cavity 25 of the device 10 and a length longer than a depth of the cavity 25, such that when the article 30 is received in the cavity 25 of the device 10, the mouthpiece 32 extends out of the cavity 25 and may be drawn on by a user, similarly to a conventional cigarette.

In use, a user inserts the article 30 into the cavity 25 of the aerosol-generating device 10 and turns on the device 10 by pressing a user button 50 (see FIG. 1 ) to activate the heater 40 to start a usage session. The heater 40 heats the aerosol-forming substrate 31 of the article 30 such that volatile compounds of the aerosol-forming substrate are released and atomised to form an aerosol. The user draws on the mouthpiece of the article 30 and inhales the aerosol generated from the heated aerosol-forming substrate 31. After activation, the temperature of the heater 40 increases from an ambient temperature to a predetermined temperature for heating the aerosol-forming substrate. The predetermined temperature is defined in the thermal profile stored in memory 28. After activation and over the course of the usage session, the control electronics 27 of the device 10 access the thermal profile stored in the memory module 28 so as to control the supply of power from the battery 26 to the heater 40 to adjust the heater temperature in accordance with the thermal profile. The heater 40 continues to heat the aerosol-generating article 30 until an end of the usage session, when the heater is deactivated and cools. In some specific examples the heater 40 may be a resistance heating element. In some specific examples the heater 40 may be a susceptor arranged within a fluctuating magnetic field such that it is heated by induction.

At the end of the usage session, the article 30 is removed from the device 10 for disposal, and the device 10 may be coupled to an external power source for charging of the battery 26 of the device 10.

The aerosol-generating article 30 for use with the device 10 has a finite quantity of aerosol-forming substrate 31 and, thus, a usage session needs to have a finite duration to prevent a user trying to produce aerosol when the aerosol-forming substrate has been depleted. A usage session is configured to have a maximum duration determined by a maximum time period from the start of the usage session. A usage session is also configured to have a duration of less than the maximum time period if a user interaction parameter recorded during the usage session reaches a threshold before elapse of the maximum time period. In a specific example the user interaction parameter is representative of a cumulative number of puffs applied to the device by a user over a usage session, with a threshold of 14 puffs defined for the cumulative number of puffs. So, for this specific example, the aerosol-generating device 10 is configured such that each usage session has a maximum duration defined by the first to occur of: i) 6 minutes from activation of the usage session, or ii) a total of 14 puffs being applied in the usage session.

In prior art devices, the thermal profile used to adjust the temperature of the heater 40 is a predetermined temperature profile which varies the target operating temperature for the heater solely as a function of the elapsed time of a usage session. FIG. 4 shows such a prior art thermal profile. The prior art thermal profile is based on the behaviour of an idealised or hypothetical user, and defines a temperature profile for the heater 40 which varies a target operating temperature for the heater 40 solely as a function of elapsed time. The prior art thermal profile of FIG. 4 is constructed on the assumption that a user applies each successive puff to the device 10 at intervals of 30 seconds, resulting in a usage session having a duration of 6 minutes (360 seconds). These hypothetical or idealised puffs are represented by dashed lines in FIG. 4 .

The operation of the device 10 using the prior art thermal profile of FIG. 4 is now described for three different scenarios:

In a first scenario, a user activates the device 10 by pressing user button 50 to start a usage session with an unused article 30 and then applies a series of 12 successive puffs spaced apart from each other at intervals of 30 seconds. As the user is applying puffs at a rate which conforms to the assumptions made for the thermal profile of FIG. 4 , the battery 26 (under the control of the control electronics 27) would provide power to the heater 40 for a usage session of 6 minutes, corresponding to 12 puffs spaced 30 seconds apart. In essence, the heater 40 would be adjusted in accordance with the thermal profile shown in FIG. 4 . As a result, the aerosol-forming substrate 31 would be substantially depleted of aerosol.

In a second scenario, the user activates the device 10 by pressing user button 50 to start a usage session with an unused article 30. However, in contrast to the first scenario, after taking the first puff at 30 seconds from the start of the usage session, the user applies all subsequent puffs spaced apart from each other at intervals of only 15 seconds. This higher puff rate results in the usage session being terminated early by the device 10 for the reason that the threshold limit of 14 puffs is reached before the elapse of 6 minutes (360 seconds) in the usage session. The effect of the increased puffing rate on heater temperature over the course of this reduced length usage session can be seen in FIG. 5 , with each applied puff represented by a dashed line. In this second scenario, as the thermal profile assumes successive puffs are applied at a time interval of 30 seconds, the effect of a real-life user applying puffs at a faster rate of one puff every 15 seconds is that the heater 40 never attains the temperatures needed in the second half of the usage session to extract all aerosol from the aerosol-forming substrate 31.

In a third scenario, the user activates the device 10 by pressing user button 50 to start a usage session with an unused article. However, in contrast to the second scenario, after taking the first puff at 30 seconds from the start of the usage session, the user then applies all subsequent puffs spaced apart from each other at intervals of only 11 seconds. As shown in FIG. 6 , this higher puff rate results in the usage session being terminated by the device 10 even earlier than for the second scenario. Again, early termination of the usage session occurs for the reason that the threshold limit of 14 puffs is reached before the elapse of 6 minutes (360 seconds) in the usage session. The effect of the further increased puffing rate on heater temperature over the course of this reduced length usage session can be seen in FIG. 6 , with each applied puff represented by a dashed line. As can be understood from FIG. 6 , the consequences of inadequate heating of the aerosol-forming substrate 31 by the heater 40 are even more severe for this third scenario than they were for the second scenario of FIG. 5 .

FIGS. 5 and 6 can therefore be seen to illustrate the problems of use of a known thermal profile for a heater which varies target operating temperature for the heater 40 solely as a function of elapsed time.

FIG. 7 illustrates a method 100 in accordance with the present disclosure. The method 100 is performed by the aerosol-generating device 10 of the present disclosure when a user applies a series of puffs to the aerosol-generating device 10 during a usage session. In step 101, an applied puff is associated with a corresponding target operating temperature for the heater 40 based on the cumulative puff count of the applied puff in the usage session. In step 102, for the applied puff, the supply of power from the battery 26 is controlled by the control electronics 27 so as to adjust the temperature of the heater 40 to the target operating temperature associated with the applied puff.

Steps 101, 102 of method 100 are performed for each of puffs applied by the user in the usage session, until termination of the usage session. The method 100 thereby enables the temperature of the heater 40 to be adjusted as a function of the cumulative puff count in a usage session.

The method 100 would be performed by a combination of the control electronics 27 and a thermal profile stored in the memory module 28. In the course of a usage session, the control electronics 27 would access the memory module 28 to read the thermal profile, and then control the supply of power from the power supply 26 in order to adjust the temperature of the heater 40 according to instructions provided in the thermal profile. However, the thermal profile employed by method 100 is different to the prior art thermal profile described above in relation to FIGS. 4 to 6 .

FIG. 8 illustrates an example of a thermal profile for use in performing the method 100 with aerosol-generating device 10. However, in contrast to the prior art thermal profile described previously, the thermal profile of FIG. 8 defines a target operating temperature for the heater 40 as a function of puff count. So, for the thermal profile of FIG. 8 , each puff of a usage session is associated with a given target operating temperature for the heater 40. The thermal profile of FIG. 8 defines a target operating temperature for each puff of a predetermined distribution of 12 puffs. As stated above, the thermal profile is stored inside the memory module 28 of the aerosol-generating device 10. When a user applies each puff of a series of puffs to the device 10, the control electronics 27 access the memory 28 to read the thermal profile. The control electronics 27 then control the supply of power from the battery 26 to the heater 40 to adjust the target operating temperature for the heater in accordance with the thermal profile of FIG. 8 and the cumulative puff count of each applied puff.

FIGS. 9 and 10 show two examples of how the target operating temperature for the heater 40 is varied with time when using the thermal profile of FIG. 8 for a usage session in which a succession of puffs are applied by a user to the aerosol-generating device 10. FIG. 9 illustrates the temperature variation where the user applies puffs each spaced apart by a uniform interval, in this case of 15 seconds. FIG. 10 illustrates the temperature variation where the user applies puffs each spaced apart by a non-uniform time interval. When examining FIGS. 9 and 10 , it can be seen that use of the thermal profile of FIG. 8 results in the target operating temperature being adjusted on the basis of the cumulative puff count of the applied puff in the usage session, rather than being adjusted solely as a function of the elapsed time in a usage session. In essence, the target operating temperature for the heater 40 is adjusted by tracking the puff count of the applied puffs with reference to the thermal profile of FIG. 8 stored in the memory module 28. So, in contrast to the use of the prior art thermal profile of FIG. 4 , the thermal profile of FIG. 8 enables the target operating temperature to be increased over the second half of a usage session regardless of the rate and timing of the puffs applied by a user.

In another example, the associating of an applied puff with a corresponding target operating temperature may additionally be a function of a time interval between the applied puff and an earlier puff in the usage session. In this example, a second thermal profile corresponding to the profile shown in FIG. 8 is used. However, this second thermal profile also contains a “predetermined time spacing”, Δt_(predet). For this example, Δt_(predet) has a value of 30 seconds. The predetermined time spacing Δt_(predet) represents a hypothetical or idealised time interval between successive puffs in the thermal profile. In this example, the temperature in the thermal profile corresponding to an applied puff is itself modified dependent upon whether the actual time interval, Δt_(predet), between an applied puff and its predecessor is different to the predetermined time spacing Δt_(predet). In the thermal profile, heater temperatures T_(n), T_(n+1) are defined for successive applied puffs ‘n’ and ‘n+1’. Where a user applies puffs to the device in a usage session, if the time interval Δt_(predet) between applied puff ‘n+1’ and earlier puff ‘n’ is less than or greater than the predetermined time spacing Δt_(predet) then, the temperature in the thermal profile for puff ‘n+1’ is modified in proportion to the difference between Δt_(predet) and Δt_(predet). Expressed mathematically, the temperature of the thermal profile for puff ‘n+1’ is modified to a temperature T_(n+1) ^(modified) as follows:

$\begin{matrix} {T_{n + 1}^{modified} = {T_{n + 1} + {\left( \frac{\left( {{\Delta f} - {\Delta t_{predec}}} \right)}{\Delta t_{predet}} \right).\left( {T_{n + 1} - T_{n}} \right)}}} & {{Equation}3} \end{matrix}$

However, the modification of the temperatures of the thermal profile is subject to a predetermined threshold limit of +/−3% of the unmodified temperature. Additionally, the modification of the temperatures of the thermal profile is also subject to an absolute temperature limit of 350 degrees Celsius. In other embodiments, different values may be set for the percentage threshold limit and absolute temperature limit.

For this second thermal profile, when a user applies a succession of puffs to the aerosol-generating device 10 over a usage session, the time interval between an applied puff and an earlier puff is first determined. Then the temperature in the thermal profile corresponding to the puff count of the applied puff (for example, for puff ‘n+1’) is modified in accordance with the methodology discussed above (see equation 3). The modified temperature in the thermal profile is then used as the target operating temperature for the applied puff, with the control electronics 27 controlling the supply of power to the heater 40 so as to achieve this target operating temperature for the applied puff. If the user should happen to apply puffs at intervals equating to the “predetermined time spacing” Δt_(predet), then no modification of the temperature(s) of the thermal profile would occur for those puffs.

In yet another example, the associating of an applied puff with a corresponding target operating temperature may additionally be a function of an intensity of an earlier puff in the usage session. For this example, the intensity of a puff is characterised by the volume of aerosol generated in response to the puff. In this example, a third thermal profile corresponding to the profile shown in FIG. 8 is used. However, this third thermal profile also contains a “predetermined intensity”, which in this example is in the form of a predetermined volume. The predetermined intensity (or volume) can be thought of as representing an idealised or assumed volume of aerosol generated by each puff in the thermal profile. For this example, the thermal profile has a predetermined number, N, of puffs which are assumed applied over a usage session. The thermal profile also has a predetermined total volume, V, of aerosol produced over the course of the usage session. In this example, the predetermined total aerosol volume, V, is assumed to be generated uniformly over each of the N puffs. So, for this thermal profile each puff of the ‘N’ puffs is assumed to result in generation of the same volume, v, of aerosol, where v=V/N. This volume, v, is the predetermined intensity (or volume). In the thermal profile, heater temperatures T_(n), T_(n+1) are defined for successive applied puffs ‘n’ and ‘n+1’. If applied puff ‘n’ has an intensity stronger than assumed in the thermal profile, then the aerosol volume, v_(n), for puff ‘n’ would be greater than the predetermined volume, v. The greater than expected intensity (aerosol volume v_(n)) for puff ‘n’ would result in greater than expected depletion of the substrate in response to puff ‘n’. To compensate for the greater than expected depletion, the target operating temperature for the next puff ‘n+1’ may need to be higher than is defined in the predetermined thermal profile. Alternatively, if applied puff ‘n’ has an intensity weaker than assumed in the thermal profile, then the aerosol volume, v_(n), for puff ‘n’ would be less than the idealised volume, v, of the thermal profile. The less than expected intensity (aerosol volume v_(n)) for puff ‘n’ would result in less than expected depletion of the substrate in response to puff ‘n’. To compensate for the lower than expected depletion, the target operating temperature for the next puff ‘n+1’ may need to be lower than is defined in the predetermined thermal profile. The modification of the temperature for puff ‘n+1’ in the predetermined thermal profile can be expressed shown in equations 1 and 2 recited above, which are repeated below for completeness:

T _(n+1) ^(modified) =T _(n+1).∝

for which: T_(n+1) is the temperature initially defined in the thermal profile for puff ‘n+1’ T_(n+1) ^(modified) is the modified temperature of the thermal profile for puff ‘n+1’; and α is a correction factor applied to T_(n+1) to address the actual “intensity” of puff ‘n’. The correction factor α will vary dependent on the amount by which the volume of aerosol, v_(n), produced in response to applied puff ‘n’ is greater than or less than idealised volume v. The correction factor, α, may be expressed as follows:

$\propto {= \left\lbrack \left( {1 + {\delta.\left( \frac{v_{n} - v}{v} \right)}} \right) \right\rbrack}$

for which: δ is a scale factor, whose value may be chosen so as to increase or reduce the effect of v_(n) being different to v when modifying the initially defined temperature T_(n+1) for puff ‘n+1’ of the thermal profile.

For this third thermal profile, when a user applies a succession of puffs to the aerosol-generating device 10 over a usage session, the volume of aerosol generated by each puff is determined. Then the temperature in the thermal profile corresponding to the puff count of the applied puff (for example, for puff ‘n+1’) is modified in accordance with the methodology discussed above. The modified temperature in the thermal profile is then used as the target operating temperature for the applied puff, with the control electronics 27 controlling the supply of power to the heater 40 so as to achieve this target operating temperature for the applied puff. If the user applies puffs over a usage session each generating a volume of aerosol equating to volume v, then no modification of the temperatures of the thermal profile would occur. However, it is more probable that there will be variations in the volume of aerosol generated by each successive puff, with some or all of the applied puffs generating a volume of aerosol different to volume v.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number “A” is understood as “A”±10% of “A”. Within this context, a number “A” may be considered to include numerical values that are within general standard error for the measurement of the property that the number “A” modifies. The number “A”, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which “A” deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. 

1.-15. (canceled)
 16. A method of operating an aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising a power supply arranged to supply power to a heater during the usage session, the method comprising: using control electronics of the aerosol-generating device to: associate a puff applied in the usage session with a corresponding target operating temperature for the heater based on a cumulative puff count of the applied puff in the usage session and on a time interval between the applied puff and an earlier puff applied in the usage session, and for the applied puff, control the supply of power from the power supply in order to adjust a temperature of the heater to the target operating temperature associated with the applied puff.
 17. The method according to claim 16, wherein the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, and wherein the target operating temperature associated with the applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff.
 18. The method according to claim 17, wherein the predetermined thermal profile comprises a predetermined relationship between a puff parameter and the predetermined distribution of puffs, the method further comprising: determining if a value of the puff parameter for either or both the applied puff and an earlier puff applied in the usage session differs from a value of the puff parameter for corresponding puffs of the predetermined distribution of puffs, modifying the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using the determined difference in the value of the puff parameter, and using the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff.
 19. The method according to claim 18, wherein the puff parameter comprises one or more of: a time interval between successive puffs, an intensity of a puff, and a volume of aerosol generated from the aerosol-forming substrate in response to a puff.
 20. The method according to claim 16, wherein the earlier puff immediately precedes the applied puff in the usage session.
 21. The method according to claim 16, wherein the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined time spacing between successive puffs of the predetermined distribution of puffs, the method further comprising: determining if the time interval between the applied puff and the earlier puff differs from the predetermined time spacing between corresponding puffs of the predetermined distribution of puffs, modifying the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this time difference, and using the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff.
 22. The method according to claim 16, wherein the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on an intensity of an earlier puff applied in the usage session.
 23. The method according to claim 22, wherein the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined intensity for each puff of the predetermined distribution of puffs; the method further comprising: determining if the intensity of the earlier puff differs from the predetermined intensity for the corresponding puff of the predetermined distribution of puffs, modifying the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this intensity difference, and using the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff.
 24. The method according to claim 16, further comprising detecting the applied puff by monitoring a change in heater temperature in response to the applied puff.
 25. The method according to claim 16, further comprising terminating the usage session upon the first to occur of: i) a cumulative number of puffs applied in the usage session reaching a predetermined puff limit, or ii) the usage session reaching a predetermined maximum time duration.
 26. A nontransitory computer-readable storage medium for use in an aerosol-generating device, the nontransitory computer-readable storage medium containing instructions for performing the method according to claim 16 on the aerosol-generating device when interacting with aerosol-forming substrate.
 27. An aerosol-generating device for generating aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply arranged to supply power to a heater during the usage session; and control electronics configured to: determine a time interval between the applied puff and an earlier puff, associate a puff applied in the usage session with a corresponding target operating temperature for the heater based on a cumulative puff count of the applied puff in the usage session and on the determined time interval, and for the applied puff, control the supply of power from the power supply in order to adjust a temperature of the heater to the target operating temperature associated with the applied puff.
 28. The aerosol-generating device according to claim 27, wherein the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the aerosol-generating device being configured such that the target operating temperature associated with the applied puff is a temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff
 29. The aerosol-generating device according to claim 27, wherein the aerosol-generating device stores a predetermined thermal profile defining a variation in heater temperature over a predetermined distribution of puffs, the predetermined thermal profile comprising a predetermined time spacing between successive puffs of the predetermined distribution of puffs, and wherein the aerosol-generating device is configured to: determine if the determined time interval between the applied puff and the earlier puff differs from the predetermined time spacing between corresponding puffs of the predetermined distribution of puffs, modify the temperature of the predetermined thermal profile for the puff in the predetermined distribution of puffs corresponding to the cumulative puff count of the applied puff by using this time difference, and use the modified temperature of the predetermined thermal profile as the target operating temperature associated with the applied puff.
 30. The aerosol-generating device according to claim 27, wherein the aerosol-generating device is configured: to determine a volume of aerosol generated from the aerosol-forming substrate in response to an earlier puff applied in the usage session, and such that the associating of the applied puff with a corresponding target operating temperature for the heater is additionally based on the determined volume for the earlier puff. 